Automatic damping means in deflection circuits



March 8, 1960 H. E. THOMAS ET AL 2,927,998

AUTOMATIC DAMPING MEANS IN DEFLECTIQN CIRCUITS Filed Feb. 25, 1955 amaze/7 PEAKED SAW mOTH SYNC. PM 55 SOURCE 1 YOKE INVENTORS HARRY E- THOMASSYLVEJTER A. 05 MARS AGENT in series with the charging capacitor.

AUTOMATIC DAMPING MEANS IN" DEFLECTION cnzcurrs Harry E. Thomas,Montclair, and Sylvester A. DeMars, Ridgewood, N.J., assignors toInternational Telephone and Telegraph Corporation, Nutley, N.J., acorporation of Maryland a t .Appli cation February 25, 1955, Serial No.490,472

' 1 Claimsl Cl. 250-27 This invention relatesv to deflection circuitsfor cathode ray type electron discharge devices and more particularly toa means for automatically damping oscillations due to reversalof sweepvoltages in the output transformer of I deflection waveform generatorsemployed in television and like apparatus.

. This is due to thetinductive kickf or voltage across the primarywinding inductance. This may cause ringing or oscillatory currents whichmay carry over into the sweep periodrand affect signal reproduction.'

- The oscillatory currents established in the output transformer uponreversal of the sweep voltage has in the past been 'dampedby employingthe plate resistance of the v tooth waveform into a trapezoidal form bywhat is known commonly asfpeaking. This peaking has been accomplished inthe past inthe sawtooth generator discharge tube circuit ,by adding afixed resistance peaking resistor The addition of this fixed resistor toa conventional sawtooth generator produces an additional pulse which issuperimposedupon the retrace portion of, the deflecting waveform. -Thisaddedpulse determines the plate resistance of the output or driver tubeof the deflection system during the retrace portion and the start of thesweep portion of the deflecting waveform to establish thedamping elfecton,the oscillations present in the output transformer.

The amount of damping provided by the driver tube is rather critical.Too much or too little damping will not have the desired effect ofsuppressing the unwantedoscillations and may affect the retrace timelong enough to pulses is present, when a given set of tubes areemployed,

when a given value of B'| voltage is present, and for receiver, thechange of anyone of these conditions ora ,combination of theseconditions will vary'the amount 2,927,998 Eatented Mar. 8, i960 biasvoltage of the peaking electron discharge device proportional to thepeak amplitude of the deflection waveform appearing at the output of thedeflection system so that automatically the correct amount of dampingresults,

regardless of the signals passingthrough the system.

A further feature of this invention is the employment i of a peakdetector to monitor the peak amplitude of the deflection waveformappearing at'the'output of the deflection system, the output of the peakdetector adjusting the bias of the peaking electron discharge devicedisposed in serial relation with the charging condenser of asawtooth.generator to provide a variable peaked sawtooth output therefrom toadjust the plate resistance of the output tube in a manner to maintain aconstant damping effect on the oscillations within. the outputtransformer deflection system. The above-mentioned and other featuresand objects 'of'this invention will become more apparent by reference tothe following description taken'in conjunction with the accompanyingdrawing, the sin'gle figure of which illustrates schematically anembodiment of our invention.

' In the drawing, there is illustrateda portion of a deflection circuitcomprising a sourceiiof pulses 1 wherein the output therefrom, asillustrated by curve 2, is repetitious ata predetermined rateforcontrol" of the operation of a trapezoidal waveform generator 3. Forpurposes of explanation, the portion of the deflection circuitillustrated is thatof a vertical deflection circuit employed ina'television receiver'and the' o utput of source 1 is repetitious at thefield scanning rate. It is to be understood that the automatic dampingcircuit disclosed herein may be utilized inany comparable deflectionsystem having a similar damping problem; v

- The trapezoidal waveform generator 3 'inclildestherein a normallynon-conducting electrondischarge-device or tube 4 and an RC timeconstant including charging con denser 5, load resistorfi and the plateresistance of electron discharge device ortube-7. Resistor 6 also servestosupply voltage from'the B -jsupply to the anode 8 of'tube 4. When apositive synchronizing pulse from source 1 is coupled through condenser9 to grid 10 of tube 4, the tube becomes conductive. The capacitor 5 atthis time immediately discharges to ground through regardless oftheamplitude of' the signals within'the the internal plate resistance oftube 4. Tube 4 behaves a certain setting'of the heightcontrol in atelevision I like a switch-between condenser 5 and ground. When thesynchronizing pulse is removed, grid'10 returns to some negativepotential cutting off tube 4 and thereby terminating the discharge ofcondenser 5. Condenser 5 of damping presented to the oscillations in theoutput transformer.- a v r Therefore, itis an object of this inventionto provide a means to automatically maintain a constant damping of theoscillations occurring in the output transformer of a deflection system.t i' I Another objectof this invention is to provide an electronically"controlled trapezoidal waveform generator which'gwill automaticallyprovide a constant damping of the oscillation mime output transformer.

featu'rs of invention is the provision .of a varistarts to chargetowardthe value of the B+ supply at aneXponential-" rate dependingprimarily upon the values of condenser 5:;and resistor 6. v

Tube 7 is placed in series with condenser 5 toprovide a variable peakingresistor by controlling its conduction and, hence, its plate resistance.The anode potentialfor tube 7 is provided by resistor 11 disposedbetweenthe B+ supply and the anode 12 of tube 7. .With tube 7 biased to obtaina given plate resistance, the output of generator 3 is coupled frompoint 13 through condenser :lfi to grid 15 of the output electrondischarge device 3 a of tube 16 substantially in the form as indicatedby waveform 17. The peaked sawtooth or trapezoidal waveform will beamplified by tube 1.6 and coupled to the primary winding 18 of theoutput transformer 19. To enable the desired automatic control of thedamping effect accomplished by the plate resistance of tube 16, a vacuumor semiconductive diode 20 is placedacross the secondary winding 21 ofoutput transformer 19. The diode 20 functions as a peak detector whoseconduction varies in accorclance with the value of the positive pulsesoccurring in the secondary winding 21. When the amplitude of the outputsignal increases, the diode 20 conducts a greater current and develops acontrol signal in the form of a positive bias voltage across resistor22. This bias v l a e ac n i u 7 to increa e t nd ct er t re? nd hu decea its Pla e r t n e- T decre ed plate e is an e re u ts in a ecreasedamoun 9? P akin n the t anczcida wa ef m Th e re s t aci litt d c the pa d pa t es cfthe defl t on age pr id s a ce rcti e dam n eff c by risin t e 91?? l e 011 r 15 of 15? 6- T s nc a h c nd fimi' e t ush and us i a l w r pl resistance for tube 16.

Conversely, a signal amplitude decrease at the secondary winding 21 willdecrease the conduction through diode 20, thus, a less positive voltageacross resistor 22, and, hence, a less positive bias on grid 23 of tube7. This results in less conduction through device 7 and an increase inplate resistance therein. A higher plate resistance for tube 7 producesan increased peaking pulse at point 13 which will bias grid 15 of tube16 more negative resulting in decreased conduction through tube 16 andthus an increase in its plate resistance to provide the necessarycorrective damping. This maintenance of constant effective plateresistance assures correct damping on the output transformer 19.

The action above outlined may seem opposite to what may at first beinferred. However, this is reconciled by the fact that as the sawtoothamplitude is increased, the damping effect is also increased due to thetendency of tube 16 to draw anode current under higher voltages. Thedamping due to plate resistance is a dynamic quantity which depends uponthe characteristics of tube 16 during the retrace period. At this time,two pposin actions take place. First, grid 15 is being driven negativeby the combined sawtooth and peaking pulse, the

net result being an increase of plate resistance. Second, the addedeffect of the peaking pulse produces a relatively high induced voltageacross anode 2 4 of tube. 16. This voltage tends to produce a decreasein plate resistance particularly it anyanode current flows. The decreaseplate resistance due to the induced voltage at anode 2 t overshadqws anyincrease of plate resistance due to the action of the driving waveformat grid 15.

The above-described automatic damping circuitwill result in a constantdamping effect of the oscillation occurring in the output transformer ofa deflectionwaveform generator due to the sudden reversal of sweepcurrents therein regardless of amplitude signal variations occurring inthe deflection waveform generator. This constant damping provides theadvantage of a deflection waveform having uniform retrace and sweeptime;

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the'objects thereof and inthe accompanying claims. i

l. A circuit for generating the. deflection voltage for adeflection'system of a cathode ray type electron dis-- charge devicewhich automatically maintains a constant damping of the oscillations insaid defiection system comprising a source of repetition pulse signals,a reactive means to produce a sawtooth waveform having a sllb 4stantially linear sweep portion and a retrace portion in synchronismwith said pulse signals, a variable resistance means coupled to saidreactive means to provide a series circuit to peak said sawtoothwaveform during the retrace portion thereof, said series circuit beingcoupled in shunt relation to said source, an output means including anelectron discharge device for coupling the peaked sawtooth waveform fromsaid reactive means, a detector means coupled to the output of saiddischarge device to develop a control signal in accordance with the peakamplitude of said peaked sawtooth waveform, and means to couple saidcontrol signal to said variable resistance means.

2. A waveform generating circuit for a deflection system of a cathoderay type electron discharge device comprising a source of synchronizingpulse signals, a time constant network including a condenser and avariable resistor, said variable resistor being coupled to saidcondenser to provide a series circuit, said series circuit being coupledin shunt relation to said source, means responsive to said pulse signalsto synchronously charge and discharge said time constant network toproduce a peaked sawtooth waveform, an output circuit including anelectron discharge device to remove the peaked sawtooth Waveform fromsaid time constant network for coupling to a deflection system, apeakdetector coupled to the output of said discharge device fordeveloping acontrol signal in accordance with the peak amplitude of said peakedsawtooth waveform, and means to couple said control signal'to saidvariable resistor to vary the resistance thereof proportional to theamplitude level of said peaked sawtooth waveform for control of the peakamplitude of said sawtooth waveform to maintain a substantially-constantdamping of the oscillations induced in said output circuit regardless ofsignal variation in said time constant network.

3. A waveform generating circuit for a deflection system of a cathoderay type electron discharge device comprising a source of synchronizingpulse signals, a reference potential, a time constant network includinga charging condenser and a first electron discharge device having atleast an anode, a cathode and a control grid, the cathode of said firstdevice being coupled to said reference potential and the anode of saidfirst device being coupled-to one side of said condenser, means coupledto the other side of said condenser and responsive to said pulse signalsto synchronously charge and discharge said time constant network toproduce a peaked sawtooth waveform, an output circuit including asecondelectron discharge device to remove the peaked sawtooth waveform fromsaid time constant network for coupling to a defiection system, a peakdetector coupled to the output of said second discharge device fordeveloping a control voltage in accordance with the peak amplitude ofsaid peaked sawtooth waveform, and means to couple said control voltageto the control grid of said electron discharge device to vary the plateresistance thereof inversely proportional to the amplitude level of saidpeaked sawtooth waveform for control of the peak amplitude of saidsawtooth waveform to maintain a substantially constant damping of theoscillations induced in said output circuitregardless of signalvariations in said time constant network.

4. A waveform generating circuit for a deflection system of a cathoderay type electron discharge device comprising a source of synchronizingpulse signals, a reference potential, a time constant network includinga condenser and an electron discharge device having at waveform, anoutput circuit to remove thepeaked sawtooth waveform from said. timeconstantmetwork for coupling to a' deflection system, a unidirectionaldevice and a resistorcoupled in a series relationship acrossfthe outputof said output circuit for developing a control voltage in accordancewith the peak amplitude 'of said peaked sawtooth waveform, and aconductor coupled to the junction of said unidirectional device andsaidresistor to couple said control voltage to the. control grid ofsaidelectron discharge device to vary the plate resistance thereof inverselyproportional to the amplitudelevel of said peaked sawtooth waveform forcontrol of the peak amplitude of said sawtooth waveform to maintaintasubstantially constant damping of. the oscillations induced in saidoutput circuit regardless of signal variations in said time constantnetwork.

5. A circuit for generating the deflection voltage for a deflectionsystem of a cathode ray type electron discharge device whichaufomatically maintains a constant damping of the oscillations insaiddeflection system comtron-discharge device having at least an anode,cathode electron discharge device to render said first electrondisprising a first electron discharge device having at least an anode, acathode and a control grid, said first.elec-' cathode of said firstelectron discharge device, a series circuit including a chargingcondenser and a variable resistancemeans coupled between the anode ofsaid first electron discharge device and said reference potential, saidload resistor and said variable resistance means providing the chargingpath for said charging condenser, a source of synchronizing pulsesignals, means coupling said synchronizing pulse signals to the cathodeof said first electron discharge device to render said first electrondischarge device conductive in synchronism with said synchronizingpulse. signals, the conductive path of said first electron dischargedevice and said variable resistance means providing the discharge pathfor said charging condenser to produce a peaked sawtooth waveform, anoutput means including a second electron discharge device and an outputtransformer to remove the peaked sawtooth waveform from the anode ofsaid first electron discharge device, the plate resistance 'of saidsecond electron discharge device damping the oscillations in said outputtransformer, peak detector means coupled to said output transformer todevelop a control signal in accordance with the peak amplitude of saidpeaked sawtooth waveform and means to couple said control signal to saidvariable resistance means to vary the resistance thereof inverselyproportional to the amplitude level of said peaked sawtooth waveform'for control of the plate resistance of said second electrondischargedevice to main tain a substantially constant damping effect on theoscillations induced in said output transformer regardless of signalvariations in the signal at the anode of said first electron dischargedevice.

6. A circuit for generating the deflection voltage for a deflectionsystem of a cathode ray type electron discharge device whichautomatically maintains a constant damping of the oscillations in saiddeflection system comprising a first electron discharge device having atleast an anode, a cathode and a control grid, said first electrondischarge device being normally nonconductive, an anode voltage supplysource, a reference potential, a load resistor coupled between saidvoltage supply source and the anode of said first electron dischargedevice, a bias resistor coupled between said reference potential and thecathode of said first electron discharge device, a series circuitcoupled between the anode of said first electron discharge deviceandsaidfreference potential, said series circuit including a chargingcondenser and a second eleccharge device conductive'in synchronism withsaid synchronizing pulse signals, the conductive path of said firstelectron discharge device and said second electron discharge deviceproviding the discharge path for said charging condenser to produce apeaked sawtooth waveform, an output means including a third electrondischarge device having at least a cathode, an anode and a control gridand an output transformer coupled to the anode of said third electrondischarge device to remove the peaked sawtooth waveform from the anodeof said first electron discharge device, the plate resistance of saidthird electron discharge device providing a damping effect for theoscillations in said output transformer, peak detector means coupled tosaid output transformer to develop a control voltage in accordance withthe peak amplitude of said peaked sawtooth waveform, and means tocouplesaid control voltage to the control grid of said second electrondischarge device to vary the plate resistance thereofvinverselyproportional to the amplitude level of said peaked sawtooth waveform foradjustment of the plate resistance of said third electron discharge.prising a first electron discharge device having at least an anode, acathode and a control grid, said first electron discharge device beingnormally nonconductive, an anode voltage supply source, a referencepotential, a load resistor coupled between said voltage supply sourceand the anode of said first electron discharge device, a bias resistorcoupled between said reference potential and the cathode of said firstelectron discharge device, a series circuit coupled between the anode ofsaid first electron discharge device and said reference potential, saidseries circuit including a charging condenser and an electron dischargedevice having at least an anode, cathode and control grid, the anode andcathode thereof being in series relationship with the chargingcondenser, said load resistor and said second electron discharge deviceproviding the charging path for said charging condenser, a source ofsynchronizing pulse signals, means coupling said synchronizing pulsesignals to the grid of said first electron discharge device to rendersaid first electron discharge device conductive in synchronism with saidsynchronizing pulse signals, the conductive path of said first electrondischarge device and said second electron discharge device providing thedischarge path for said charging condenser to produce a peaked sawtoothwaveform, an output means including a third electron discharge devicehaving at least an anode, a cathode and a control grid and an outputtransformer coupled to the anode of said third electron discharge deviceto remove device and said resistor to couple said control voltage to thecontrol grid of'said second electron discharge device to vary the plateresistance thereof inversely proportional to the amplitude level of saidpeaked sawtooth waveform for control of the plate resistance of saidthird electron discharge device to maintain a substantially constantdamping eflfect on the oscillations induced in said output transformerregardless of signal variation in the References Cited in the file ofthis patent signal at the anode of said first electron discharge device.10 2,728,875

UNITED STATES PATENTS Ames et a1. Aug. 31, 1948 Custin May 22, 1951 Wynna Nov. 6, 1951 Woodrufi Dec. 1, 1953 Volz July 27, 1954 Casey Nov. 30,1954 Kihn Dec. 27, 1955

